NASA engineers are developing a radical new form of launch that begins aboard an electrified track similar to that of a rollercoaster. (Source: NASA)

The sled would then fling a scramjet into the air, which would activate and rocket to the upper atmosphere. Once in the upper atmosphere, the scramjet would fire a capsule launch vehicle into space as the final step. (Source: NASA/Artist concept)

New launch system could be used for manned launches and satellite launches

NASA's
budget may
be cut, but that hasn't stopped the first international
organization to put a man on the Moon from dreaming big. One
key question the agency is looking at is what the next big thing in
space propulsion will be. NASA and foreign space agencies have
examined plasma
engines, ion
engines, nuclear-powered
designs, and solar
sails, but these technologies lack the impulse and thrust to
accelerate a launch vehicle into orbit.

However,
NASA's latest
proposal may be the most creative idea of them all and has
the potential to be relatively affordable. The new proposal
starts by placing a sled on electric tracks -- NASA's sled needs to reach a whopping 600 mph (appr. 1,000
km/h).

At the end of the track, the passenger vehicle, which
rests atop the sled, will be flung off, launching at extreme speed.
The passenger vehicle would be a wedge-shaped aircraft, with
scramjets aboard, which would activate upon launch. Those
scramjets would accelerate the aircraft to Mach 10.

Wings
would gradually angle the craft into the Earth's upper atmosphere.
At the boundaries of the Earth's atmosphere, the scramjet would fire
the actual spacecraft -- a capsule. The maneuver would be akin
to firing a round out of a barrel

By using mechanical motion
to launch the craft, instead of expensive chemical boosters, the cost
of launches could dramatically decrease.

NASA's Stan Starr,
branch chief of the Applied Physics Laboratory at Florida's Kennedy
Space Center, says the technology to achieve this type of launch
isn't that far away. In a released statement, he explains, "All
of these are technology components that have already been developed
or studied. We're just proposing to mature these technologies
to a useful level, well past the level they've already been taken.
Essentially you bring together parts of NASA that aren't usually
brought together."

Engineers at NASA and the U.S. Air
Force have worked on a variety of scramjet projects thus far,
including the X-43A and X-51 (a
missile design). So far these programs have had a couple
of successful launches and tests under their belt, raising
hopes that the technology can soon be applied to projects like the
launcher.

Mr. Starr and other NASA engineers have assembled a
proposal to build the system, which they're dubbing the Advanced
Space Launch System. They're seeking grants from a variety of
sources.

Under the plan Langley Research Center in Virginia,
Glenn Research Center in Ohio, and Ames Research Center in California
would build and test the parts of the hypersonic aircraft.
Dryden Research Center in California, Goddard Space Flight Center in
Maryland and Marshall, along with the Kennedy Space Center would
engineer the rail track. The plan calls for an actual two-mile
long test track to be laid down parallel to the crawlway that the
Shuttle used to be transported along to Launch Pad 39A. Mr.
Starr comments, "I still see Kennedy's core role as a launch and
landing facility."

The 10-year plan for the launch
platform calls for the program to begin with launching small drones
-- like those used by the Air Force -- into orbit. This would
be followed by satellite launches. If all goes according to
plan, the system could eventually be used for low-cost manned mission
launches, as well.

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This is excitingI thought people calculated that mass drivers are not economical on Earth

1000 km/h = 277 m / s so it's way below escape velocity so they still need chemical fuel while in air. Rocket can propel a shuttle from 0 to 277m/s in 15 seconds assuming 20m/s^2 acceleration. So all they saved is about 10 seconds of fuel? Of course this is very rough calculation as mass is expelled from rocket making acceleration faster with less fuel.

The real problem is the speed of sound is ~760mph at sea level. They're proposing to accelerate the "wedge" to ~600mph and expect scramjets to light? You need to be going around mach 4 to get an effective scramjet startup. Less than Mach 2 and you don't even really want a ramjet. This doesn't even account for the absolutely RIDICULOUS dynamic pressures an air/spacecraft would have to endure traveling > mach 1 (or 3-4 for a low speed scramjet startup) at sea level.

The real problem is the speed of sound is ~760mph at sea level. They're proposing to accelerate the "wedge" to ~600mph and expect scramjets to light? You need to be going around mach 4 to get an effective scramjet startup. Less than Mach 2 and you don't even really want a ramjet. This doesn't even account for the absolutely RIDICULOUS dynamic pressures an air/spacecraft would have to endure traveling > mach 1 (or 3-4 for a low speed scramjet startup) at sea level.

The mass driver is there just to get up to the minimum operating speed for the scramjet. By itself, it doesn't save much fuel.

The scramjet stage does most of the work of accelerating to escape velocity. Since it's an air-breathing engine, you don't need to carry oxidizer, just fuel. That dramatically cuts down on launch weight.

Then the spacecraft itself is kicked into orbit by pushing away the scramjet stage (which is itself reusable, I assume) or by chemical rocket.

High energy microwave antennas on either side of the tracks that focus down the line ahead of the launch vehicle should easily do the trick of keeping the launch vehicles safe from any birds & in dramatic fashion I might add. =)

Yup. The scramjet will save a lot of fuel. It's the only realistic near future technology that can significantly reduce the cost of launching something into orbit.

Doing a back of the envelope calculation, a 1000m/s launch track + mach 10 scramjet will reduce the amount of fuel needed to reach mach10 by a factor of 2.2 allowing for either a much smaller total rocket or a much larger upper stage + payload combination. At mach 25 (slightly under orbital velocity of mach28.5) the ratio increases to 6.5:1. At mach 28.5 the ratio goes up to 8.3:1 but this would be undercut somewhat due to the need for a circularizing rocket burn once the ship reached space (otherwise it's in a ballistic missile type orbit and would reenter shortly after leaving the atmosphere).

As back of the envelope math these calculations ignore various fiddly bits that can significantly alter the final results. The relative mass of the ramjet vs conventional rocket module would be a major factor in where the actual numbers end up. For a real world example a large chunk of the higher performance of hydrogen rockets over kerosene or solid fuel rockets is lost because cryogenic hydrogen is bulky and the larger fuel tanks increase the parasitic mass of the rocket itself.

For anyone curious about my math, the rocket equation when solved for the mass ratio is:

deltaV (kerosene rocket) is 3400, 8500, or 9700m/s in the three cases above.

deltaV (kerosene ramjet) is 2400, 7500, or 8700m/s (remember the ramjet is leaving the launch track at 1000m/s).

Specific impulse (Isp) is a measure of how long 1kg of propellant can produce a thrust of 1g. Since only ~28.1% of the propellant in a kerosene rocket is kerosene (the remainder is oxygen) a ramjet, by getting its oxygen from the air, will have 3.56 as much kerosene per kg of propelant and be able to burn for 3.56x as long giving an Isp of 350*3.56 ~= 1250s.

PLugging the numbers above into the rocket equations gets mass ratios of 1.22, 1.84, and 2.03 for the scramjet vs 2.69, 11.88, and 16.86 for the conventional rocket. These numbers divided by each other are what I cited in the 2nd paragraph.

That 10 seconds of fuel is probably about 20 times less total volume though. The scramjet has very efficient fuel/thrust/aerodynamic lift ratio, and a new lightweight vehicle will not be trying to drive 4,250,000 lbs directly perpendicular to gravity (rough shuttle weight @ liftoff).

I think the idea is that the cannon launch gets them up to a speed that a SCRAM jet can work. SCRAM jets are nice because unlike rockets they are air breathing, they need to take fuel up but not an oxidizer to burn it with.

There are a lot of downsides, only some of which are addressed by a mass driver launch. First is that they can only work at extremely high speeds, you need to boost them up to those speeds using some other engine technology. Second is that no one has ever flown one anywhere close to orbital speed (Mach 25 about). Finally, even if you can reach orbital speed you still need a relatively small rocket to actually insert yourself into orbit, since the SCRAM jet uses air as its oxidizer you can't use it at orbital altitudes.

The Fabio pic is rather appropriate- Just because it's technically possible for a passenger vehicle to be accelerated to 600mph and then "flung off" at the end of the track (along with a fueled launch vehicle to make up the other 15,000mph) doesn't mean it's the best way to fly.